I've had the same problem with the same truck in the past couple of weeks.
First thing I found is that a 6000kv + motor is waaaaay to powerful for the truck.
The second thing I found was that the ball diff was destroyed - the holes where the balls go were non existent - just four really big holes
, the other gears were fine (in my case). The thrust bearing had also collapsed.
I bought a new diff gear and a ball diff rebuild kit and the truck is now running better than it ever has! I am now using a 19t brushed modified motor with a 2S Lipo and still lifts the front wheels off the ground.
My advise would be, rebuild the diff and dial back on the power
Good luck!